(a) Field of the Invention
The present invention relates to an electric car. More specifically, the present invention relates to a device and method for charging a battery of an electric car.
(b) Description of the Related Art
Different from an internal combustion engine driven car, an electric car moves using the limited energy of a battery comprised of modules. When the energy is exhausted, the battery must be charged with external power.
A state of charging (SOC) indicates a ratio of amount of usable current (or charge) over an induced (or charged) amount of current. The SOC of each module of the battery of the electric car varies depending on initial manufacture specifications, temperature and impedance of the modules, or the amount of continuous charging and discharging cycles.
A conventional battery charging method is divided into three modes. In the first constant power or CP mode, the battery is initially charged over a predetermined level of voltage using full power. In the second constant current or CC1 mode, the battery is charged with a 9 ampere (A) current. In the third CC2 mode, the battery is charged with a 4.5 A current.
However, when a car driver disconnects the charging plug during the charging process, or when the charging process is interrupted because of an abnormal power system condition, an undercharge occurs. An undercharge is also generated when the charging process is interrupted because of high internal resistance of the battery modules.
Therefore, the undercharge reduces capacity of the battery, and thereby, decreasing performance of the car.